46 lines
1.4 KiB
C
46 lines
1.4 KiB
C
/*****************************************************************************\
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* compute_ip_checksum.c
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* $Id$
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\*****************************************************************************/
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#include <stdint.h>
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#include "ip_checksum.h"
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/* Note: The contents of this file were borrowed from the coreboot source
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* code which may be obtained from http://www.coreboot.org.
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* Specifically, this code was obtained from coreboot (LinuxBIOS)
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* version 1.0.0.8.
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*/
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unsigned long compute_ip_checksum(void *addr, unsigned long length)
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{
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uint8_t *ptr;
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volatile union {
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uint8_t byte[2];
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uint16_t word;
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} value;
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unsigned long sum;
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unsigned long i;
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/* In the most straight forward way possible,
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* compute an ip style checksum.
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*/
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sum = 0;
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ptr = addr;
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for(i = 0; i < length; i++) {
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unsigned long value;
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value = ptr[i];
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if (i & 1) {
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value <<= 8;
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}
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/* Add the new value */
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sum += value;
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/* Wrap around the carry */
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if (sum > 0xFFFF) {
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sum = (sum + (sum >> 16)) & 0xFFFF;
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}
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}
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value.byte[0] = sum & 0xff;
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value.byte[1] = (sum >> 8) & 0xff;
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return (~value.word) & 0xFFFF;
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}
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